CS184 Hw4 Writeup

Haoqing Xuan 3036149505

Maodun Zhang 3035626112

Part 1:

Implementation overview:

Firstly, we reserve memory for our point masses. Then, for a horizontal orientation, we go

through each row and column, figuring out where each point mass should be placed. Similarly,

for a vertical orientation, we add randomness to the z-axis. We also check if any points are

pinned by iterating through the pinned vector. Lastly, we create springs by checking the index of

the point masses and then we add the corresponding springs into the arrays.

This is the result of scene/pinned2.json, where we can clearly see the cloth wireframe and the

structure of point masses and springs.

Here is the wireframe:

Part 2

When we change the ks to a lower value, we can observe that the springs seem to change from

the 4 pinned corners first and then gradually move toward the center of the sheet. And the corner

seems sharper as if there’s a string under the sheet to hold the corner up.

Below are image of having density of 100 g/cm^2, and we can see that the image with high

density has more obvious curve at the center of the sheet, as if a heavier object is placed at the

center that drags the sheet down. When we have low density, 5 g/cm^2, the influence on the

sheet is much less and the surface around the pinned corners are much smoother. Another

intersting fact is that if we decrease the density and immediately start simulation, the sheet seems

to “bounce back” since less pressure is on the surface.

Below are the images of changing damping values, with low damping values like 0.06, the center

of the sheet seems less curved compared to the image with high damping values, 0.8. However,

to human eyes, the effect of changing damping values is not as obvious as changing other

parameters. The third image is the sheet with 0.2 damping value.

Below are the pictures of scene/pinned4.json using only default parameters from different angles.

Part 3

Image of ks = 500 N/m scene/sphere.json

Part 5:

Shaders are isolated programs that run in parallel on GPU, executing sections of the graphics

pipeline, taking in an input, and outputting a single 4-dimensional vector. We know that vertex

shaders are shaders that apply transforms to vertices by modifying their geometric properties like

position and normal vectors, writing the final position of the vertex to gl_Position in addition to

writing varyings for use in the fragment shader. And the fragment shaders are what we get after

rasterization, which these shaders process. Fragment shaders generally take in geometric

attributes of the fragment calculated by the vertex shader to compute and write color into

out_color.

The Blinn-Phong shading model is a lighting model used in computer graphics to simulate how

light interacts with surfaces. It consists of three main components. Firstly, ambient Light

provides a constant color contribution to the surface, representing overall scene lighting. Diffuse

Reflection models light scattering on rough surfaces, determining the base color of objects based

Blinn-Phong Shader

scene/sphere.json - Diffuse Lighting

scene/sphere.json - Blinn-Phong Lighting

Custom texture

Custom Texture - continued

scene/sphere.json - Custom texture

Bumping

scene/sphere.json - Bumping

Mirror

scene/sphere.json - Mirror